I either have my Steam Deck docked and use mouse and keyboard or I have my Steam Deck sitting up in handheld and us the right track pad as a mouse and use my wireless keyboard

Not sure the default controller is fully functional and I can imagine the on-screen keyboard covers a lot of the screen area so I find it easiest to use the Steam Deck docked or in handheld propped up with the track pad as a mouse and a keybaord connected

It is also possible to just use the keyboard connected and tab through the menus without having to touch the trackpad at all also